What's the best way to remove the rust / prep the surface?

I picked up a wire cup brush with a 1/4", but it's limited to 4,500 RPM. My tool options are a 1/8" collet Dremel (won't fit), 1/4" die grinder (20,000+ RPM), and a battery drill (600 RPM, and under-performing when I tried it).

Can I limit the die grinder's speed by limiting the air pressure and still have it be usable?

Do I just need to go buy something else entirely?

What should I do for the best chance at a good paint application?

I already have a can of color-matched paint in a rattle can.

Must I apply primer first? How many coats?

Is there a particular kind / concern about applying it?

Not relevant to this particular job, but is there a difference in the primer I'd use for metal vs. plastic?

2 Answers
2

A wire brush is the best option for removing surface rust, but I wouldn't try the brush you have in any of the tools you've got!

In terms of painting, you can just use normal primer, but I would go for a rust inhibiting one (e.g. those sold by Bilt Hamber, Hammerite and others) - If it has started rusting there, there is a reason for it (usually stonechips), so you might as well try and prevent it reoccurring. The particular primer should tell you how many coats to use, but I normally go for around three thin ones.

Metal primers are different to plastic ones, as they often incorporate a slight acid to bond better with the surface.

In addition to all the points made by @NickC - unless you have a huge expanse of rust, a handheld wire brush might be better than anything else.

I usually keep my cars for a very long time, and this being Scotland - they rust. A lot! So I just keep on top of the sills, arches etc with wire brushes - use them at the first sign of rust and expose the metal back a good inch all round the rust spot; prime it up and respray.

Always worth keeping an old tin of your car paint to help get matching colour next time.